Remarks on 

 Prieftlcy's 



and Count 

 Rumr'oriTs ex- 

 periments. 



]58 ON THE VEGETATION OF PLANTS. 



Count Rum- Count Rumford made an attempt, in the year 1787, td 



ments to Wain overthrow the doctrine of the purification of the air by plants, 

 oxigeo from wa- His arguments were, that leaves confined in water were in 

 ter y olarhg t. unnatura i circumftances, and that pure air could be obtained 

 from other bodies, as fine (pun glafs, raw filk, common cot- 

 ton, and that of the poplar tree, expofed in water to the light 

 of the fun*. | 



The ingenious author of Phytologia alfo fays, it may be fuf- 

 peded that, in many of the experiments of Prieftley and In- 

 genhouz, the production of vital air might be (imply owing td 

 the action of the fun's light on the water in which the vege- 

 tables were immerfed, like that from the filk in the experiments 

 of Count Rumford; and that the fine points or (harp edges of 

 thefe bodies, contributed only to facilitate the liberation of it 

 when expofed to the fun fhine, which thus dilbxigenated the 

 water by their united effect. 



The experiments of Count Rumford are far from being 



fatisfactory. Thirty grains of raw filk, at the end of three 



days, yielded him but 3J cubic inches of air, and fometimes 



four days elapfed before a fufficient quantity could be collected 



for an experiment. 



Dirrft experi- In order to find how much air could be obtained from the 



xncnts a £ ne points or ftarp edges" of certain bodies acting upon 



water, the following fubftances were expofed one day to the 



action of folar light, in forty ounce meafures of pump water. 



with fibrous bo- Filaments of afbeftos, baked horfe-hair, common cotton, and 



dies, which gave ^ ^ p t | ie a f c j ep | as Syriaca, the flower panicles of rhus cotinus, 

 air lefs in quan- * J . r . 



tity and purity the fine hairy plumes of chmatis crifpa, the ipikes of panicum 

 than leaves. glaucum, and charcoal in powder. From each of thefe fub- 

 ftances, from two to four drachm meafures of pure air were 

 obtained, which devoured nearly two meafures of nitrous air 5 

 confequently it was lefs pure than that procured from leaves 

 expofed in the fame water. There was alfo a much fmaller 

 quantity of it; for from eight to nineteen drachm meafures 

 may be obtained in a few hours, by immerfing. the leaves of 

 any plant in the fame water, and expeiing theci to folar light. 

 Other fourcss of Some water, without any mixture, will yield ovigenous gas 

 air- by the combined action of light and heat; and many fubftances 



placed in water, appear to act merely by railing its temper- 

 ature. 



* Tranfaflions cf the Royal Society for 1787. 



The 



